From patchwork Mon Sep 30 05:59:25 2019

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X-Patchwork-Submitter: Masahiro Yamada <yamada.masahiro@socionext.com>

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From: Masahiro Yamada <yamada.masahiro@socionext.com>

To: linux-arm-kernel@lists.infradead.org,

        Russell King <rmk+kernel@armlinux.org.uk>

Cc: Linus Torvalds <torvalds@linux-foundation.org>,

        Olof Johansson <olof@lixom.net>, Arnd Bergmann <arnd@arndb.de>,

        Nick Desaulniers <ndesaulniers@google.com>,

        Nicolas Saenz Julienne <nsaenzjulienne@suse.de>,

        Masahiro Yamada <yamada.masahiro@socionext.com>,

        Julien Thierry <julien.thierry.kdev@gmail.com>,

        Russell King <linux@armlinux.org.uk>,

        Stefan Agner <stefan@agner.ch>,

        Thomas Gleixner <tglx@linutronix.de>,

        Vincent Whitchurch <vincent.whitchurch@axis.com>,

        linux-kernel@vger.kernel.org

Subject: [PATCH] ARM: fix __get_user_check() in case uaccess_* calls are not

 inlined

Date: Mon, 30 Sep 2019 14:59:25 +0900

Message-Id: <20190930055925.25842-1-yamada.masahiro@socionext.com>

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KernelCI reports that bcm2835_defconfig is no longer booting since

commit ac7c3e4ff401 ("compiler: enable CONFIG_OPTIMIZE_INLINING

forcibly"):

  https://lkml.org/lkml/2019/9/26/825

I also received a regression report from Nicolas Saenz Julienne:

  https://lkml.org/lkml/2019/9/27/263

This problem has cropped up on arch/arm/config/bcm2835_defconfig

because it enables CONFIG_CC_OPTIMIZE_FOR_SIZE. The compiler tends

to prefer not inlining functions with -Os. I was able to reproduce

it with other boards and defconfig files by manually enabling

CONFIG_CC_OPTIMIZE_FOR_SIZE.

The __get_user_check() specifically uses r0, r1, r2 registers.

So, uaccess_save_and_enable() and uaccess_restore() must be inlined

in order to avoid those registers being overwritten in the callees.

Prior to commit 9012d011660e ("compiler: allow all arches to enable

CONFIG_OPTIMIZE_INLINING"), the 'inline' marker was always enough for

inlining functions, except on x86.

Since that commit, all architectures can enable CONFIG_OPTIMIZE_INLINING.

So, __always_inline is now the only guaranteed way of forcible inlining.

I want to keep as much compiler's freedom as possible about the inlining

decision. So, I changed the function call order instead of adding

__always_inline around.

Call uaccess_save_and_enable() before assigning the __p ("r0"), and

uaccess_restore() after evacuating the __e ("r0").

Fixes: 9012d011660e ("compiler: allow all arches to enable CONFIG_OPTIMIZE_INLINING")

Reported-by: "kernelci.org bot" <bot@kernelci.org>

Reported-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>

Acked-by: Arnd Bergmann <arnd@arndb.de>

Tested-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>

Tested-by: Fabrizio Castro <fabrizio.castro@bp.renesas.com>

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>

---

 arch/arm/include/asm/uaccess.h | 8 +++++---

 1 file changed, 5 insertions(+), 3 deletions(-)

diff --git a/arch/arm/include/asm/uaccess.h b/arch/arm/include/asm/uaccess.h

index 303248e5b990..559f252d7e3c 100644

--- a/arch/arm/include/asm/uaccess.h

+++ b/arch/arm/include/asm/uaccess.h

@@ -191,11 +191,12 @@ extern int __get_user_64t_4(void *);

 #define __get_user_check(x, p)						\

 	({								\

 		unsigned long __limit = current_thread_info()->addr_limit - 1; \

+		unsigned int __ua_flags = uaccess_save_and_enable();	\

 		register typeof(*(p)) __user *__p asm("r0") = (p);	\

 		register __inttype(x) __r2 asm("r2");			\

 		register unsigned long __l asm("r1") = __limit;		\

 		register int __e asm("r0");				\

-		unsigned int __ua_flags = uaccess_save_and_enable();	\

+		unsigned int __err;					\

 		switch (sizeof(*(__p))) {				\

 		case 1:							\

 			if (sizeof((x)) >= 8)				\

@@ -223,9 +224,10 @@ extern int __get_user_64t_4(void *);

 			break;						\

 		default: __e = __get_user_bad(); break;			\

 		}							\

-		uaccess_restore(__ua_flags);				\

+		__err = __e;						\

 		x = (typeof(*(p))) __r2;				\

-		__e;							\

+		uaccess_restore(__ua_flags);				\

+		__err;							\

 	})

 #define get_user(x, p)							\